‘Almost three years ago,’ Lila replied.

Agata couldn’t hide her disappointment. ‘And no one’s tried to take it any further?’ She’d put ten years of her life into the diagram calculus, and the whole physics community had spurned the approach.

‘The lack of progress isn’t from a want of trying,’ Lila insisted. ‘And you shouldn’t take it personally. It’s got nothing to do with the quality of your work or the way it’s been received. The problem is far more widespread than that.’

Agata was mollified, but still confused. ‘What problem?’

‘We’ve all hit a dead patch,’ Lila said sadly. ‘Chemists, biologists, astronomers, engineers. Since they switched on the messaging system, there hasn’t been a single new idea across the mountain.’

‘You mean no one’s been sending back new ideas?’ Agata had predicted as much – but surely that self-censorship hadn’t surprised anyone.

‘Oh, the messages have contained no innovations,’ Lila confirmed. ‘But neither has the work itself.’

‘I don’t understand,’ Agata admitted.

Lila said, ‘If people did innovate, the results would leak back to them one way or another. I know you believed that they’d be able to keep quiet, so everything would go on as usual. But everything has not gone on as usual. We’ve had no new ideas since the system was turned on – because if we’d had them, we would have heard of them before we’d had a chance to think of them ourselves. The barriers to information flow are so porous now that the knowledge gradient has been flattened: the past contains everything the future contains . . . which means the future contains nothing more than the past.’

Agata was stunned. If this was true, the messaging system had undermined the whole reason for the mountain’s existence. Every generation before her had advanced their understanding in one field or another. What would her own generation be famous for? Rendering the creation of new knowledge impossible.

She dragged herself out of the dismal fantasy. To have lost three years was appalling, but the disaster would be self-limiting in the end.

‘So how long does this go on?’ she asked Lila.

‘About a dozen more stints.’

That would be five stints after the Surveyor returned. ‘I’m surprised people didn’t act sooner.’ The self-censorship hypothesis predicted an absence of news of future innovations – but news of their absence could have been sent back as soon as the dire situation was apparent. ‘I suppose it’s the writing we found on Esilio that tips the balance in the end?’ Agata suggested. ‘The system could hardly have been shut down before the Surveyor returned with that discovery, if it’s a crucial element in swinging the vote.’

Lila said, ‘The system isn’t shut down by a vote.’